Grouping the pages

Is it possible to group two pages under parent page, so that parent page physically does not exist. Basically to write something in frontmatter like:

menu (somehow to define the main menu) :
   parent (the item which is virtually created but actually does not exis):
      child1: slug (page which is paced in user/pages/child1)
      child2: slug (page which is paced in user/pages/child2)

So basically these two child items are placed in the user/pages, but they are grouped in the menu like they were placed under the: user/pages/parent/child1 and user/pages/parent/child2.

What i am trying to achieve, is that the parent is not accessible and actually does not exist.

Just create a parent/ folder. It will create a virtual page. You simply need to just edit the page and set it so that it's not routable and not visible. it will not show up in the menu then.

Ok, thank you, but how i do this? Maybe anything at wiki?

https://learn.getgrav.org/content/routing but how to make it invisible at all? even in breadcrumbs?

Check the docs for Page Content Headers

Should be:

routable: false
visible: false

Although looks like breadcrumbs needs to be updated so that it doesn't provide a link for non-routable pages: https://github.com/getgrav/grav-plugin-breadcrumbs/blob/develop/templates/partials/breadcrumbs.html.twig

Thank you!